1. Field of the Invention
The present invention relates to a method of measuring the pattern shift occured in epitaxial growth on a semiconductor wafer with patterns thereon and more particularly to a method of measuring the pattern shift with a high accuracy in a short period of time.
2. Description of the Prior Art
It is essential to control the shift of a buried diffusion pattern after the growth of an epitaxial layer in a bipolar transistor in an IC. For this purpose, the growth conditions (such as reaction temperature and reaction speed) should be always controlled to assure constant pattern shift. However, it is very difficult to control the growth conditions strictly enough to meet the requirement of constant pattern shift because frequent measurement of the pattern shift is inevitable.
Conventionally, the angular polishing and stain etching method is used for this purpose. This method comprises: (1) slicing chips as samples having a buried layer in parallel to and perpendicular to the orientation flat by using a dicing saw; (2) angular polishing of the new narrow surfaces created as sections of the sliced chips; (3) etching the polished surfaces (Sirtl, 2 to 3 seconds); and (4) measuring the shift of the patterns of the buried layers by using differential, interference microscope.
The pattern shift factor is obtained by the following equation: ##EQU1##
However, since it takes more than three hours to measure the pattern shift, this conventional method cannot be used so frequently and is rather expensive.